Simplified battery powered regenerative drive system

ABSTRACT

A battery powered regenerative drive system having a time ratio controlled regenerative chopper circuit for regulating electrical power flow between the drive system battery and traction motor in both the drive and regenerative modes of the drive system, and a novel and simplified mode switching arrangement utilizing only two switches, which may be either unidirectional solid state switches or contacts of a single pole double throw relay, for switching the drive system between its drive and regenerative modes.

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SHEH 2 0? 2 as l CONTROLLER I 50 I ERROR 54 32o DETECTORiDII r)BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates generally to battery powered, including hybrid battery powered,electrical drive systems of the kind which utilize a time ratiocontrolled chopper circuit to regulate electrical power flow through thesystems. The invention relates more particularly to such a drive systemwhich is operable in both a drive mode and a regenerative mode andembodies a novel mode switching arrangement for switching between theseoperating modes.

2. Prior Art The critical need to reduce air pollution has sparkedrenewed interest in electrical and hybrid electrical drive systems forautomobiles and other vehicular applications. Classically, these drivesystems were intially implemented with electromechanical contactors andlossy rehostates. Such drives are characterized by various disadvantageswhich are well known .to those versed in the art and need not bediscussed here. Suffree it to say that some of these disadvantages aregradually being overcome in industrial vehicles applications byreplacement of the rheostats by thyristorized controls. Most of thesethyristorized controls, however, do not have bi-directionalcharacteristics and are hence not capable of operation in a regenerativemode as is hightly desirable if not absolutely essential in passengervehicle applications.

US. Pat. No. 3,566,717 discloses a hybrid battery powered drive systemwhich is capable of regeneration, that is capable of operation in both adrive mode and a regenerative mode. In the drive mode, the tractionmotor of the drive system is powered from the battery to propel thevehicle. In the regenerative mode, the motor is driven as a generatorfrom the road to both deliver charging current to the battery andproduce an electromagnetic braking torque on the vehicle.

The patented drive system embodies a solid state time ratio controlledregenerative chopper circuit through which electrical power flows fromthe battery to the motor in the drive mode and from the motor(generator) to the battery in the regenerative mode. In each mode, powerflow is controlled by regulating the duty cycle, i.e. by proportioningthe conduction time to the blocking time of the chopper circuit, toregulate driving torque in the drive mode and braking torque andbattery. charging current in the regenerative mode. The duty cycle isthus regulated by manipulation of a throttle pedal having anintermediate mode transfer position. Depression of the pedal throughthis mode transfer position shifts the drive system from theregenerative mode to its drive mode. Release of the pedal for reversemovement or retraction through the mode transfer position shifts thedrive system from its drive mode to its regenerative mode.

In the drive system of the patent, mode shifting in response to movementof the throttle pedal through its mode transfer position is accomplishedby a number of electromechanical relays. 'Such a multirelay modeswitching arrangement has certain disadvantages.

Among the foremost of these is relatively low transfer speed betweendrive and regenerative modes, relatively large weight and volume of therelays, relatively high cost, and relatively short service life.

The earlier mentioned copending application also discloses a batterypowered regenerative drive system capable of operation in drive andregenerative modes.

SUMMARY OF THE INVENTION The present invention provides a batterypowered regenerative drive system which utilizes a solid state timeratio controlled regenerative chopper circuit to control electricalpower flow between the battery and traction motor in both the drive andregenerative modes of the drive system and embodies a novel simplifiedmode switching arrangement for switching the drive system between thesemodes. This switching arrangement uses only two active mode transferswitches, one in series and one in parallel with the traction motorarmature, in combination with a few additional passive unidirectionalsolid state devices to accomplish the mode switching function. The modeswitching function is carried out in such a way that the mode transferswitches operate between their conducting and blocking states only inthe dry switching mode, that is at zero or very low current levels.Accordingly, the switches need not be rated for power handling, that isfor power and current interruption, but rather only for voltage blockingand current conduction. In this regard, the mode transfer switches willbe recognized by those versed in the power handling art as trueswitches, in contrast to breakers and switchers which are power handlingdevices, and possess the usual advantages of smaller size, lesserweight, lower cost, etc., compared to power handling devices.

Two embodiments of the invention are disclosed. One embodiment is asingle relay system wherein the mode transfer switches are the contactsof a single pole double throw relay. The other embodiment is an allsolid state system wherein the mode transfer switches are solid statedevices, namely SCRs. A unique feature of the latter embodiment residesin the fact that the chopper circuit of the'drive system embodies apower SCR switch controlled by a commutating network to accomplish thepower chopping or pulsing function of the chopper, and this commutatingnetwork also performs the tum-off function necessary to effect switchingof the mode transfer SCR switches between their conducting and blockingstate's. v

BRIEF DESCRIPTION OFTHE DRAWINGS FIG. 1 schematically illustrates asingle relay battery powered regenerative drive system according to theinvention; and

FIG. 2 schematically illustrates an all solid state battery poweredregenerative drive system according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS from the battery to drive themotor armature. In the regenerative mode, the motor is driven as agenerator, such as during downhill coasting of a vehicle propelled bythe drive system, to charge the battery and produce an electromagneticbraking torque on the motor armature.

Motor 12 is a d.c. motor such as a series type d.c. motor rated for highspeed operation and has an annature l6 and field 18. Since this motorproduces driving torque in the drive mode and braking torque in theregenerative mode, it is hereafter referred to as a torquer.

Power control unit 14 includes a time ratio controlled regenerativechopper circuit 20, mode switching means 22, diodes 24, 26, 28, 30, anda manual control 32. Chopper circuit 20 has an SCR (Silicon ControlledRectifier) power switch 34, a commutating circuit 36 for the powerswitch, and a switch controller 38 which supplies gating signals to thepower switch and commutating circuit to actuate the power switch to itsconducting and blocking states alternately. In the ensuing description,the terms ON and OFF are used to designate the conducting and blockingstates of the power switche as well as the other SCR switches referredto later. in both the drive and regenerative modes of the drive system,switching of the power switch 34 between its ON and OFF states effectsenergy transfer between the battery 10 and torquer 12 in re- 1 petitiveenergy transfer cycles. During each cycle, the power switch remains ONfor a time I and OFF for a time t The chopper circuit 20 has a dutycycle a which is defined as the ratio of the switch ON time (I to thetotal cycle time T (t t i.e.

a ON/ Energy transfer between the battery 10 and motor 12 is regulatedby regulating this duty cycle.

Mode switching means 22 cooperates with the diodes 24, 26, 28, and 30 toestablish the operating mode of the drive system. The mode switchingmeans are operable to a drive condition or configuration to place thedrive system in its drive mode and to a regenerative condition orconfiguration to place the drive system in its regenerative mode.

Manual control 32 commands or controls the duty cycle of the choppercircuit 20 and thereby energy transfer between the battery 10 andtorquer 12 to command driving torque in the driving mode and brakingtorque in the regenerative mode of the drive'system. The control alsoactuates the mode switching means 22 between drive and regeneration.

As will appear from the ensuing description, the mode switching means 22and diodes 24, 26, 28, and 30 have a unique arrangement whichconstitutes the subject matter of the present invention. Thisarrangement enables the mode switching function to be accomplished witha minimum number of relatively low cost, small size, light-weightcircuit elements including only two active switches which need be ratedonly for voltage blocking and current conduction, not power handling andcurrent interruption. These switches may be the contacts of one singlepole double throw relay (FIG. 1) or solid state switching means such assilicon controlled rectifiers (FIG. 2). Accordingly, it will beunderstood that the term switches" are used inthe present disclosure inthe same sense as is customary in the electrical transmission art todenote voltage blocking and current conduction switching devices incontrast to power handling current interruption switching devices, suchas switches or breakers.

Except for the improved mode switching means 22, the present drivesystem is similar to that disclosed in the earlier mentioned copendingapplication. Briefly, in operation of the present drive system, thepower switch 34 is actuated between its ON and OFF states with a dutycycle a commanded by the manual control 32. When the power switch is ONin the drive mode, the torquer 12 is powered by energy stored in thebattery 10, and current flow occurs through. the drive system in thedirections indicated by the solid line arrows labeled C (conducting) toproduce an electromagnetic driving torque on the torquer armature 16 andstore electrical energy in the torquer field 18. When the power switchis OFF in the drive mode, the energy stored in the fielddischargesthrough the armature to produce current flow in the directions indicatedby the solid line arrows labeled B (blocking). This current flow-occursthrough the armature in the same direction as when the power switch isON to produce continued driving torque on the armature.

In the regenerative mode of the drive system, the torquer 12 is drivenas a generator, such as during downhill coasting of a vehicle powered bythe drive system, and the power switch 22 is again actuated between itsON and OFF states alternately. When the power switch is ON, the torquerproduces current flow through the drive system in the directionsindicated by the broken line arrows labeled C to store energy in thetorquer field 18 and produce an electromagnetic braking torque onthe-armature 16. When the power switch is OFF, current flow occurs inthe directions indicated by the broken line arrows labeled B to effectcharging of the battery 10 by the combined output energy from thetorquer and stored energy in the torquer field and produce a brakingtorque on the armature.

Referring now in more detail to the drive system of FIG. 1, thecommutating circuit 36 includes a commutating SCR switch 39, acommutating capacitor 40, a linear inductor 42 with its directionalrectifier 44, a saturating reactor 46, and a precharge circuit 48. Inboth the drive and regenerative modes of the drive system, the capacitor40 is initially charged through the precharge circuit 48. When thecommutating SCR 39 is turned ON by application of a low power signal toits gate from controller 38, with the power switch 34 in its ON state,capacitor 40 discharges through the linear inductor 42 while thesaturating reactor 46 is blocking and resetting magnetically. The linearinductor 42 and capacitor 40 form a resonant circuit which oscillates atthe resonant frequency of the circuit. During this oscillation, thepower stored in capacitor 40 is transferred to the linear inductor 42which, in turn, delivers the power to the capacitor in a reversedirection. This oscillation establishes the common node of the capacitor40 and the saturating reactor 46 at a voltage approximately equal andopposite to the battery voltage. Thus, when the saturating reactorsaturates, the power switch 34 and the commutating switch 39 aresubjected to a reverse voltage across their terminals. This reversesequence by applying gating signals alternately to the gates of switches34, 39.

Manual control 32 comprises a throttle pedal 50 movable between a fullyreleased or retracted maximum braking torque position and a fullydepressed or extended maximum driving torque position through anintermediate mode transfer position. For convenience, the range of pedalpositions between the fully retracted and mode transfer positions isreferred to as the braking range. The range of pedal positions betweenthe mode transfer and fully depressed positions is referred to as thedriving range. Throttle pedal 50 operates a torque command signal source52, such as a rheostat, which produces a torque command signalrepresenting driving or braking torque, as the case may be, related tothrottle pedal position. Thus, when the throttle pedal is depressedthrough its driving range from mode transfer position, the signal source52 produces a torque command signal representing increasing drivingtorque. When the throttle pedal is released to retract through itsbraking range from mode transfer position, the signal source produces atorque command signal representing increasing braking torque.

In accordance with the invention disclosed in the aforementionedcopending application, the torque command output of the torque commandsignal source 52 is fed to an error detector 54. Error detector 54receives a second input from a current sensor 55 in series with thetorquer field 18. This sensor produces an output proportional to thecurrent flow through the field. The output of error detector 54 is asignal representing the difference between the sensor and torque commandsignals to the detector. This output signal is fed to the switchcontroller 38. Switch controller 38, which may be a pulse widthmodulator or comprise a clock pulser and variable time pulser like thosedisclosed in U.S. Pat. No. 3,566,717, has outputs connected to the gatesof power switch 34 and commutating switch 39. The switch controllerfeeds to the power and commutating switches gating signals for gatingthe switches ON and OFF in such a way as to establish a duty cycle arelated to the amplitude of the input signal to the controller. Morespecifically, the controller feeds to the power switch 34 a gatingsignal having periodic gating pulses which gate the power switch ON andfor a period t proportional to the amplitude of the controller inputsignal. The controller feeds to the commutating switch 39 a gatingsignal having periodic gating pulses which occur between the gatingpulses to the power switch and gate the commutating switch ON andthereby the power switch OFF for a period such that each power switchtime, t pulse and the following power switch time OFF, t pulse have atotal or combined period T.

Except for the improved mode switching means 22, the drive system asdescribed to this point is generally similar to that disclosed in theaforementioned copending application. This improved mode switchingmeans, which constitutes the subject matter of the present invention,will now be described.

Mode switching means 22 comprises a pair of switches 56, 58 which, inthe particular drive system shown in FIG. 1, are the normally open andnormally closed contacts, respectively, of a selflatching single poledouble throw mode control relay 60. Relay 60 has a voltage coil 62 andzero current dropout coils 64, 66. Relay coil 62 is connected to anenergizing source through a switch 68 actuated by the throttle pedal 50.Switch 68 closes to energize the relay coil 62 upon depression of thethrottle pedal through its mode transfer position toward its drivingrange and opens to deenergize the coil upon retraction of the pedalthrough its mode transfer position toward its braking range. The relaycurrent coils 64, 66 sense current flow through the relay contacts 56,58. Coil 66 actuates normally closed lockout contacts 69 in serieswith-coil 62. In the ensuing description, the normal positions(illustrated) of the relay contacts 56, 58 are referred to as theirregeneration positions. The positions occupied by the contacts when therelay coil 62 is energized (i.e., contacts 56 closed and contacts 58open) are referred to as their drive positions. Relay current coil 66 isreferred to as a drive current sensor and current coil 66 as aregeneration current sensor which opens contacts 69 in response tocurrent flow through the sensor.

The operation of the drive system will now be described assuming thethrottle pedal 50 to be initially in its fully released or retractedposition with the vehicle stationary. Under these conditions the modecontrol relay contacts 56, 58 occupy their illustrated regenerationpositions, lockout contacts 69 are closed, the torquer armature 16 isstationary, and no current flow occurs in the drive system.

Assume now that the throttle pedal is depressed through its modetransfer position to a final position in its driving range correspondingto a selected driving torque. As the pedal passes through its modetransfer position, it actuates the pedal switch 68 to shift the modecontrol relay contacts 56, S8 to their drive positions and feeds to theerror detector a torque command signal which progressively increases toa level representing the selected driving torque commanded by the finalpedal position. The error detector also receives from the current sensor55 a signal proportional to the current flow through the torquer field18 and hence to the actual driving torque developed by the torquer. Theoutput from the error detector is proportional to the difference betweenthe torque command and current sensor input signals to the detector.This output from the error detector activates the switch controller 38which then feeds gating signals to the power switch 34 and commutatingswitch 39 for gating the power switch ON and OFF in the manner explainedearlier.

Each time the power switch 34 gates ON with the mode control relaycontacts 56 and 58 in drive position, current flow occurs in thedirections of the solid line arrows C in FIG. 1. As shown, this currentflow is from the battery 10, through the contacts 56, torquer armaturel6, diode 24, drive current sensor 64, torquer field l8, and powerswitch 34, back to the battery. This current flow produces a drivingtorqueon the torquer armature and stores electrical energy in thetorquer field. Each time the power switch gates OFF, the stored energyin the torquer field 18 discharges to produce current flow through thedrive system in the directions indicated by the solid line arrows B.This current flow occurs from the field, through the diode 28, which isa flyback diode, mode control relay contacts 56, torquer armature 16,diode 24, and drive current sensor 64, back to the field to produce acontinued driving torque on the armature.

Accordingly, depression of the accelerator pedal 50 to a selecteddriving position results in substantially continuous current flowthrough the torquer 12 for accelerating a vehicle powered by the drivesystem with a driving torque corresponding to the final pedal position,as explained more fully in the earlier mentioned copending application.Release of the throttle pedal for return toward its mode transferposition causes a reduction in current flow through and driving torquedeveloped by the torquer 12 to effectdeceleration of the vehicle.regard,

Assume now that the throttle pedal 50 is released for return through itsmode transfer position to a selected position within its braking range.The torquer armature 16 is then driven in a generator mode from the roadby the inertia of the vehicle and, in the case of downhill coasting ofthe vehicle, by the additional action of the gravitational force on thevehicle. As the throttle pedal passes through mode transfer position,the pedal switch 68 is actuated to deenergize the mode control relaycoil 62. However, the relay contacts 56, 58 remain in their drivepositions by virtue of the holding action of the relay drive currentsensor 64 and until the current flow through this sensor drops to zeroor some preset low level compatible with the rating of the relay. Atthis point, the relay contacts are released to return to their normal orregeneration positions of FIG. 1. In this regard, attention is directedto the earlier discussion wherein it was noted that the swtiches orcontacts 56, 58 need be rated only for voltage blocking and currentconduction and not for power handling and current interruption.

With the throttle pedal 50 held at a selected position in its brakingrange and the mode control relay contacts 56, 58 in their regenerationpositions of FIG. 1, the power switch 34 is again gated ON and OFF witha duty cycle a related to the pedal position, as explained more fully inthe copending application. Each time the power switch gates N, currentflow occurs through the drive system in the directions of the brokenline arrows C in FIG. 1. This current flow occurs through the torquerarmature 16, mode control relay regeneration contacts 58, theregeneration current sensor 66, torquer field 18, power switch 34, anddiode 26 back to the armature to store energy in the field. Each timethe power switch gates OFF, the power generated by driving of thetorquer armature 16, as well as the energy stored in the torquer field18, is delivered to the battery 10 to charge the battery. In this OFFstate of the power switch, current flow occurs in the directions of thebroken line arrows B through the armature 16, relay regenerationcontacts 58, regeneration current sensor 66, torquer field 18, flybackdiode 28 back to thebattery. Operation of the torquer 12 in thisgenerator mode produces an electromagnetic braking torque on the torquerarmature corresponding to the braking position of the throttle pedal, asexplained more fully in the copending application. The current flowthrough sensor 66 retains the lockout contacts 69 open.

If the throttle pedal is again depressed through its mode transferposition to a selected position in its driving range, the mode controlrelay 60 is again actuated to its drive condition to effect driving ofthe torquer armature 16 by the battery 10 in the manner explainedearlier. During this mode transfer, however, the relay contacts 56, 58initially remain in their regenerative positions owning to current flowthrough the regeneration current sensor 66 which retains the lockoutcontacts open to prevent energizing of the relay coil 62. When thecurrent flow through the sensor 66 decays to zero or a low level, thelockout contacts 69 reclose, to energize relay coil 62 and the relaycontacts 56, 58 shift to their drive positions. Diode 30 provides avoltage regulating action for protecting the torquer 12 againstgenerating voltages higher than battery voltage and thereby causingimproper operation.

The solid state drive system of FIG. 2 is identical to the single relaysystem of FIG. 1 except for replacement of the mode control relay 60 bysolid state switches 56a, 58a, such as thyristors, and a pair ofselflatching single pole double throw relays 60a, 61a, and replacementof the throttle pedal switch 68 by a single pole double throw switch 68afor controlling the relays.

The gate terminals of switch 560 are connected to a gating voltagesource through normally open contacts 70a of relay 60a. The gateterminals of switch 58a are connected to a gating voltage source throughnormally open contacts 72a of relay 61a. Relays 60a, 61a have voltagecoils 74a, 76a connected to an energizing source through the pedalswitch 68a and zero current dropout coils 78a, 80a connected to thedrive system circuit in the same manner as the current coils of the modecontrol relay in FIG. 1. Coils 78a, 80a actuate normally closedinterlock contacts 82a, 84a in series with the relay voltage coils 76a,740, respectively. For convenience, relays 60a, 61a are shown separatelyfrom the switch controller 68. In actual practice, however, the relaysmay be embodied in the controller.

In the following description, switches 56a, 58a; relay contacts 70a,72a; relay voltage coils 74a, 76a; and relay current coils 78a, 80a arereferred to as drive and regeneration switches, drive and regenerationcontacts, drive and regeneration coils, and drive and regenerationcurrent sensors, respectively.

The solid state drive system operates in the same manner as the singlerelay drive system of FIG. 1 except for the manner in which the solidstate drive system is switched between its drive and regenerative modes.Thus, in the solid state drive system, when the throttle pedal 50 is inits braking range, the pedal switch 68a is positioned to energizeregeneration relay coil 76a and close its contacts 72a for applying agating voltage to the regeneration switch 58a and thereby placing thelatter switch in its conducting state. Current flow then occurs throughthe drive system in the same directions as indicated by the broken linearrows B, C in FIG. 1 to charge the battery 10 and produce brakingtorque on the torquer armature 16. This current flow occurs throughregeneration current sensor 80a to open interlock contacts 840 andprevent energizing of drive relay coil 74a. When the throttle pedal isin its driving range, the pedal switch is positioned to energize relaydrive coil 74a and close relay drive contacts 70a for applying a gatingvoltage to the drive switch 56a and thereby placing the latter switch inits conducting state. Current flow then occurs through the drive systemin the same directions as indicated by the solid line arrows B. C inFIG. 1. This current flow occurs through drive current sensor 780 toopen interlock contacts and prevent energizing of regeneration relaycoil 76a.

During operation of the drive system, when the throttle pedal isdepressed through its mode transfer position from its braking range intoits driving range to accelerate, the relay regeneration coil 76a isdeenergized and the relay drive coil 74a is energized to open the relayregeneration contacts 72a and close the drive relay contacts 704.However, these relay contacts do not immediately open and close owing tocurrent flow through the regeneration current sensor 80a which holds therelay contacts 72a closed and prevents energizing of the drive relaycoil until the current flow through the sensor decays to zero. At thispoint, regeneration contacts 72a and interlock contacts 84a are releasedto open and close, respectively, drive relay coil 74a is energized toclose its drive contacts 70a and open its interlock contacts 82a,regeneration switch 58a turns OFF, and a gating voltage is applied tothe drive switch 56a for turning this switch ON. A reverse action occurswhen the throttle pedal is released to re tract through its modetransfer position into its braking range to decelerate. In this case,the relay drive contacts 70a remain closed and interlock contacts 82aremain open until current flow through the drive current 78a decays tozero. The drive contacts 70a and interlock contacts 82a then open andclose, respectively, drive switch 56a turns OFF, and the regenerationrelay coil 76a reenergizes to open its interlock contacts 84a and closeits contacts 720 for turning ON the regeneration switch 58a.

What is claimed as new in support of Letters Patent l. A battery poweredregenerative drive system operable in a'drive mode and a regenerativemode, comprising:

a battery;

a direct current torquer having an armature and a field and operable asa motor in said drive mode and a generator in said regenerative mode;

a power control circuit connecting said battery and torquer fortransmitting energy from said battery to said torquer to produce anelectromagnetic driving torque on said armature in said drive mode, andtransmitting energy from said torquer to said battery to charge saidbattery and produce an electromagnetic braking torque on said armaturein said regenerative mode; and

said control circuit including first, second and third circuit legsconnected in electrical parallel and having first electrically connectedends and second electrically connected ends, and a fourth circuit legsterminally connected to said second leg at first and second junctionsadjacent said first and second leg ends, respectively, and a fifthcircuit leg terminally connected to said third and fourth legs betweenthe ends thereof, said battery being serially connected in said firstleg with its positive and negative terminals adjacent said first andsecond leg ends, respectively, said armature being serially connected insaid second leg between its first and second junctions with said fourthleg, said field being serially connected in said fifth leg, a drive modeswitch serially connected in said second leg between its first end andits first junction with said fourth leg, a diode serially 2. A drivesystem according to claim 1 wherein: connected in said second legbetween its second end and its second junction with said fourth leg forconducting current toward said second junction, a diode seriallyconnected in said third leg between its first end and its junction withsaid fifth leg for conducting current toward the latter leg end, a powerswitch serially connected in said third leg between its second end andits junction with said fifth leg, a regenerative mode switch seriallyconnected in said fourth leg between its first junction with said secondleg and its junction with said fifth leg, a diode serially connected insaid fourth leg between its second junction with said second leg and itsjunction with said fifth leg for conducting current toward said latterjunction, means for actuating said regenerative and drive mode switchesto conducting and blocking states, respectively, to condition said drivesystem for operation in the regenerative mode, and to blocking andconducting states, respectively, to condition said drive system foroperation in the drive mode, and means for periodically actuating saidpower switch between blocking and conducting states alternately for avariable time period.

said mode switches are contacts of a mode control relay means. 3. Adrive system according to claim 2 wherein: said relay means comprisesone single pole double throw relay. 4. A drive system according to claim1 wherein: said mode switches are solid state swtiches. 5. A drivesystem according to claim 4 wherein: said solid state switches aresilicon controlled rectifiers. 6. A drive system according to claim 1wherein: said switch actuating means comprise a manual control such as athrottle pedal movable between braking and driving positions through anintermediate mode transfer position, means actuated by said manualcontrol for placing said mode switches in their regenerative mode statesin response to movement of the manual control through mode transferposition into the braking range and in their drive mode states inresponse to movement of the manual control through mode transferposition into the driving range, and a time ratio controlled circuitcontrolled by said manual control for regulating the duty cycle of saidpower switch in response to movement of said manual control through said

1. A battery powered regenerative drive system operable in a drive modeand a regenerative mode, comprising: a battery; a direct current torquerhaving an armature and a field and operable as a motor in said drivemode and a generator in said regenerative mode; a power control circuitconnecting said battery and torquer for transmitting energy from saidbattery to said torquer to produce an electromagnetic driving torque onsaid armature in said drive mode, and transmitting energy from saidtorquer to said battery to charge said battery and produce anelectromagnetic braking torque on said armature in said regenerativemode; and said control circuit including first, second and third circuitlegs connected in electrical parallel and having first electricallyconnected ends and second electrically connected ends, and a fourthcircuit legs terminally connected to said second leg at first and secondjunctions adjacent said first and second leg ends, respectively, and afifth circuit leg terminally connected to said third and fourth legsbetween the ends thereof, said battery being serially connected in saidfirst leg with its positive and negative terminals adjacent said firstand second leg ends, respectively, said armature being seriallyconnected in said second leg between its first and second junctions withsaid fourth leg, said field being serialLy connected in said fifth leg,a drive mode switch serially connected in said second leg between itsfirst end and its first junction with said fourth leg, a diode serially2. A drive system according to claim 1 wherein: connected in said secondleg between its second end and its second junction with said fourth legfor conducting current toward said second junction, a diode seriallyconnected in said third leg between its first end and its junction withsaid fifth leg for conducting current toward the latter leg end, a powerswitch serially connected in said third leg between its second end andits junction with said fifth leg, a regenerative mode switch seriallyconnected in said fourth leg between its first junction with said secondleg and its junction with said fifth leg, a diode serially connected insaid fourth leg between its second junction with said second leg and itsjunction with said fifth leg for conducting current toward said latterjunction, means for actuating said regenerative and drive mode switchesto conducting and blocking states, respectively, to condition said drivesystem for operation in the regenerative mode, and to blocking andconducting states, respectively, to condition said drive system foroperation in the drive mode, and means for periodically actuating saidpower switch between blocking and conducting states alternately for avariable time period. said mode switches are contacts of a mode controlrelay means.
 3. A drive system according to claim 2 wherein: said relaymeans comprises one single pole double throw relay.
 4. A drive systemaccording to claim 1 wherein: said mode switches are solid stateswtiches.
 5. A drive system according to claim 4 wherein: said solidstate switches are silicon controlled rectifiers.
 6. A drive systemaccording to claim 1 wherein: said switch actuating means comprise amanual control such as a throttle pedal movable between braking anddriving positions through an intermediate mode transfer position, meansactuated by said manual control for placing said mode switches in theirregenerative mode states in response to movement of the manual controlthrough mode transfer position into the braking range and in their drivemode states in response to movement of the manual control through modetransfer position into the driving range, and a time ratio controlledcircuit controlled by said manual control for regulating the duty cycleof said power switch in response to movement of said manual controlthrough said ranges.